In conventional cellular wireless access networks, a cell is covered by a BTS (base station transceiver) and all mobile terminals communicate with the BTS directly. With the addition of relay transceivers, hereinafter simply “relays”, a multi-hop network including the BTS, relay nodes and mobile terminals, is set up. With relay nodes involved, the coverage of a wireless access network is improved. In such a wireless access network, there may be multiple routes for the communication between a terminal and network to take. For example a terminal can communicate directly with the BTS or indirectly via one or more relay nodes.
An example of a two-hop scenario is shown in FIG. 1. Shown is a base station 10 having a coverage area 12, and a relay 16 having a coverage area 18. There is a link 22 between the base station 10 and the relay 16 which is typically a high capacity and very reliable wireless link. Shown are a number of mobile terminals 14 communicating directly with the BTS 10, and a number of mobile terminals 20 communicating with the relay 16 which relays communications for these mobile terminals to and from the BTS 10.
In such a network, the fixed relay node 16 is added to improve the coverage in the edge of a cell/BTS. Since the relay is a fixed node, the channel between the BTS 10 and the relay can be a high quality channel implemented using any one of many advanced channel technologies, such as MIMO, which can provide improved capacity. However, the quality of the channel between the relay node 16 and a mobile terminal 20 is typically lower and less stable due to the mobility of the mobile terminal. Because of this, it is possible that data will accumulate in the relay after having been transmitted over the reliable channel between the BTS and the relay. This requires that the relay node have a significant buffer capacity, particularly in the case where a long delay bound is allowed, and there are a lot of mobile terminals that are served by the relay.